border-1px($color)
  position: relative
  &:after
    dispaly: block
    position: absolute
    left: 0
    bottom: 0
    width: 100%
    border-top: 1px solid $color
    content: ''
border-none()
   &:after
     display:none

bg-image($url)
  background-image:url($url+"@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
      background-image: url($url + "@3x.png")